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Legal TB-500

Claims, findings and the public record.

TB-500 references

Study papers and public records, from structural actin work to compounding documents.

Biology papers

For the biological starting point, there is Irobi’s actin-sequestration structure and the Goldstein review of full-length thymosin beta-4. The rat wound paper supplies a positive repair result; the dystrophin-deficient mouse study supplies the functional disappointment. The horse-sample assay concerns the identity and detection of the TB-500 fragment.

The muscle paper serves as my check on the expansive use of “regeneration”. Its strength outcome is especially useful beside the more encouraging wound findings.

Public records

The FDA safety page, bulks-list framework, July 2026 advisory meeting and interim-policy guidance address different parts of the compounding question. The WADA list addresses tested sport. The bibliography below includes the study citations and the public records.

  1. Irobi E, Aguda AH, Larsson M, et al. Structural basis of actin sequestration by thymosin-beta4: implications for WH2 proteins. EMBO J. 2004;23(18):3599-3608. ↗
  2. Bock-Marquette I, Saxena A, White MD, Dimaio JM, Srivastava D. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004;432(7016):466-472. ↗
  3. Malinda KM, Sidhu GS, Mani H, et al. Thymosin beta4 accelerates wound healing. J Invest Dermatol. 1999;113(3):364-368. ↗
  4. Morris DC, Cui Y, Cheung WL, et al. A dose-response study of thymosin β4 for the treatment of acute stroke. J Neurol Sci. 2014;345(1-2):61-67. ↗
  5. Goldstein AL, Hannappel E, Sosne G, Kleinman HK. Thymosin β4: a multi-functional regenerative peptide. Basic properties and clinical applications. Expert Opin Biol Ther. 2012;12(1):37-51. ↗
  6. Ruff D, Crockford D, Girardi G, Zhang Y. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin β4 in healthy volunteers. Ann N Y Acad Sci. 2010;1194:223-229. ↗
  7. Smart N, Risebro CA, Melville AAD, et al. Thymosin β4 induces adult epicardial progenitor mobilization and neovascularization. Nature. 2007;445(7124):177-182. ↗
  8. Smart N, Rossdeutsch A, Riley PR. Thymosin β4 and angiogenesis: modes of action and therapeutic potential. Circulation. 2008;117(15):1907-1909. ↗
  9. Bock-Marquette I, Shrivastava S, Srivastava D. Thymosin beta4 is cardioprotective after myocardial infarction. Ann N Y Acad Sci. 2007;1112:343-357. ↗
  10. Stark C, Taimen P, Tarkia M, et al. Cardioprotection by systemic dosing of thymosin beta four following ischemic myocardial injury. Front Pharmacol. 2013;4:149. ↗
  11. ClinicalTrials.gov. Thymosin beta-4 in acute myocardial infarction (NCT05984134), registered as completed; an earlier injectable thymosin β4 acute myocardial infarction trial (NCT01311518) was withdrawn before it began. (Trial-registry record establishing the absence of completed human efficacy data for the TB-500 fragment.) ↗
  12. Morris DC, Chopp M, Zhang L, Lu M, Zhang ZG. Thymosin beta4 improves functional neurological outcome in a rat model of embolic stroke. Neuroscience. 2010;169(2):674-682. ↗
  13. Peng H, Xu J, Yang XP, et al. Thymosin-β4 prevents cardiac rupture and improves cardiac function in mice with myocardial infarction. Am J Physiol Heart Circ Physiol. 2014;307(5):H741-H751. (Cardiac-rupture / function finding; the tumor-angiogenesis safety signal is reviewed in Goldstein 2012 [5].) ↗
  14. Mendias CL, Awan TM. Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance. Sports Med. 2026. ↗
  15. Sosne G, Qiu P, Kurpakus-Wheater M, et al. Activation of pro-resolving pathways mediate the therapeutic effects of thymosin beta-4. Front Immunol. 2024;15:1458684. ↗
  16. Zhang Y, et al. Tβ4-exosome-loaded hemostatic and antibacterial hydrogel to improve vascularized wound repair. Mater Today Bio. 2025;31:101585. ↗
  17. U.S. Food and Drug Administration. Bulk Drug Substances Used in Compounding Under Section 503A of the FD&C Act. FDA.gov (verified 2026-05-29). Definitions of Category 1 and Category 2 and the bulks-list / nomination framework. ↗
  18. U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding That May Present Significant Safety Risks. FDA.gov. Historical Category 2 entry for 'Thymosin beta-4, fragment (LKKTETQ), also known as TB-500,' effective with the September 29, 2023 update; FDA's page, content current as of April 22, 2026, now records the nomination as withdrawn, shows TB-500 is no longer in Category 2, and retains its safety rationale (checked September 2026). ↗
  19. U.S. Food and Drug Administration. July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee. FDA.gov (verified 2026-05-29). Public calendar listing BPC-157, KPV, TB-500, and MOTs-C as substances 'being considered for inclusion on the 503A Bulks List' — a scheduled discussion, not a decision. ↗
  20. U.S. Food and Drug Administration. Interim Policy on Compounding Using Bulk Drug Substances Under Section 503A of the FD&C Act (guidance landing page). FDA.gov (guidance finalized January 2025; verified 2026-05-29). Underlies the January 7, 2025 change to how nominated bulk substances are categorized, and the 503A/503B access framework. ↗
  21. McDermott Will & Emery. End of an Era: FDA Retires 2017 Interim Policies for Bulk Drug Lists. mcdermottlaw.com (analysis of the January 7, 2025 FDA action; verified 2026-05-29). Secondary legal analysis confirming that existing Category 1 substances retain enforcement discretion while Category 2 substances do not regain it. ↗
  22. World Anti-Doping Agency. The Prohibited List. wada-ama.org. TB-500 and thymosin beta-4 fall under prohibited peptide, growth-factor, and tissue-repair categories, banned in and out of competition; detected by LC-MS anti-doping assays in equine and human matrices. ↗
  23. Cha HJ, Jeong MJ, Kleinman HK. Role of thymosin beta4 in tumor metastasis and angiogenesis. J Natl Cancer Inst. 2003. ↗
  24. Zhang Y, et al. Thymosin beta 4 is overexpressed in human pancreatic cancer cells and stimulates proinflammatory cytokine secretion and JNK activation. Cancer Biol Ther. 2008. ↗
  25. Ho EN, et al. Doping control analysis of TB-500, a synthetic version of an active region of thymosin β4, in equine urine and plasma by liquid chromatography-mass spectrometry. J Chromatogr A. 2012. ↗
  26. Spurney CF, et al. Evaluation of skeletal and cardiac muscle function after chronic administration of thymosin beta-4 in the dystrophin deficient mouse. PLoS One. 2010. ↗
  27. Delcourt V, et al. TB500/TB1000 and SGF1000: A scientific approach for a better understanding of misbranded and adulterated drugs. Drug Test Anal. 2023. ↗